In the well known “lost wax” process of investment casting, a fugitive or disposable wax pattern is made by injection molding melted wax in a die corresponding to the configuration of the article to be cast. Typically, each wax pattern includes integral wax gating. A plurality of such molded wax patterns then are joined to a common wax runner bar by wax welding the gating to the runner bar. A frusto-conical or other wax pour cup typically is wax welded to the runner bar to complete the pattern assembly. The pattern assembly is invested in a ceramic shell mold by repeatedly dipping the pattern in a ceramic slurry, draining excess slurry, stuccoing with coarse ceramic particles or stucco, and air drying until a desired thickness of a ceramic shell mold is built-up on the pattern assembly. The pattern assembly then is removed from the green shell mold typically by heating the shell mold to melt out the pattern assembly, leaving a ceramic shell mold which then is fired at elevated temperature to develop appropriate mold strength for casting a molten metal or alloy.
In the past, the wax patterns have been wax welded manually to the wax runner bar. Such manual wax welding is disadvantageous in that it is time consuming and costly as a result and also produces pattern assemblies that exhibit high variability from one pattern assembly to the next with respect to dimensional locations of the patterns on the runner bar and the strength of the wax weld between the pattern gating and the runner bar from one pattern to the next on the runner bar. Improper pattern positioning on the runner bar and breaking off of some patterns at the wax weld can occur.
An object of the invention is to provide a fugitive pattern and method of making a fugitive pattern assembly for use in the lost wax precision investment casting process that overcome the above disadvantages.
Another object of the invention is to provide apparatus for manipulating a fugitive pattern to position it relative to another component of a pattern assembly.
Another object of the invention is to provide an investment casting having features adapted to be engaged by a manipulator.